Apparatus for reducing contamination in apparatus using deep ultraviolet (UV) light (e.g., having a 193 nm wavelength) such as actinic mask inspection systems or deep UV lithographic systems are known. Since these systems operate at atmospheric pressures, ventilation systems relying on the flow of air at atmospheric pressure have been used to reduce the effects of contaminants.
By contrast, extreme ultraviolet (EUV) light (e.g., having a 13.5 nm wavelength) actinic mask inspection systems or EUV lithographic systems operate in vacuum or near-vacuum conditions because EUV light is not sufficiently transmitted by air at atmospheric pressure. Accordingly, conventional contamination control systems using a flow of air are not suitable for EUV systems.
Various contamination protection apparatus for use with EUV light have been proposed but have had only limited success. For example, contamination protection using vacuum pumping has been proposed but has not been adequate and has not been capable of providing protection in areas in close proximity to optical components, such as near surfaces of optics, masks or detectors. Another proposed apparatus uses cross-flow gas jets. Such systems use high-speed gas flow directed nominally parallel to a surface of a component to blow away or deflect contaminants; however the high speed flow of gas can produce density gradients that degrade the imaging performance of a subject optical system.